In the next-generation mobile communication, carrier frequency is expected to increase with an expansion of the frequency band used. An increase in the carrier frequency can increase a propagation loss of radio waves, which in turn can reduce the cell size. In order to realize the same degree of coverage as the conventional coverage, it is necessary to increase the number of base station apparatuses. This, however, will increase the cost. Thus, a system in which a relay station apparatus is provided between a base station apparatus and a mobile station apparatus has been considered. As the mobile station apparatus may communicate not with the base station apparatus at a remote location but with the relay station apparatus, it is possible to significantly reduce the transmission power, which is problematic on an uplink, in particular.
Non-Patent Document 1 proposes a system that is suitable for the adaptive modulation techniques using relay station apparatuses. In this system, a mobile station apparatus that has a good propagation channel state with the base station apparatus performs downlink data communication through high-efficiency data modulation such as 64 QAM (Quadrature Amplitude Modulation), while a mobile station apparatus that has a bad propagation channel state with the base station apparatus performs downlink data communication through low-speed data modulation such as QPSK (Quadrature Phase Shift Keying).    Non-Patent Document 1: Ryo Hasegawa, Raiz Esmailzadeh, Hoang Nam Nguyen, and Masao Nakagawa: “Multi-hop System for Adaptive Modulation using Regenerating Fixed Hop Stations,” TECHNICAL REPORT OF IEICE, RCS2004-210